States' rights and slavery
Anyone defending the idea that the people of the states in America have the right to decide their own laws on matters not explicitly assigned to the federal government in the U.S. Constitution will almost inevitably have someone appear, like the zombie in the Woods– Murphy videos , moaning, "Slavery!" What is amusing here is that such zombies have things exactly backwards: there was no national consensus to outlaw slavery, and the only thing enabling some parts of the United States to be free of this egregious institution was... states' rights! It was only the fact that northern states could ban this practice unilaterally that created a large block of the country where slaveholding interests did not have political power, thus enabling the elimination of slavery in the entire country. Hat tip to historian Joseph Stromberg for his advice on this post. UPDATE: And of course, sometimes, states' rights were employed to enable bad things, like segregation in the An...